1. Field of the Invention
The present invention relates to an elastic wave device for use in a resonator, a band pass filter, or the like. More particularly, the present invention relates to an elastic wave device including a piezoelectric thin film made of LiTaO3 and a filter device including the elastic wave device.
2. Description of the Related Art
WO12/086639 discloses an elastic wave device in which a high acoustic velocity film, a low acoustic velocity film, a LiTaO3 film, and an IDT electrode are stacked on a support substrate in that order. According to WO12/086639, a leaky wave that propagates through the LiTaO3 film is used.
Japanese Unexamined Patent Application Publication No. 2000-286663 discloses a surface acoustic wave resonator in which an electrode made of Al is provided on a 15°-rotated Y-cut X-propagation LiNbO3 film. In this surface acoustic wave resonator, a straight line connecting distal ends of first electrode fingers of the IDT electrode and a straight line connecting distal ends of second electrode fingers of the IDT electrode extend obliquely with respect to a surface-acoustic-wave propagation direction at an angle of about 18° to 72°.
The elastic wave device described in WO12/086639 has a problem that the frequency characteristic thereof has transverse-mode ripples.
According to Japanese Unexamined Patent Application Publication No. 2000-286663, the transverse mode reflected by one busbar and that reflected by the other busbar cancel each other to reduce the transverse mode.
However, in the elastic wave device in which an elastic wave is confined by using a high acoustic velocity film as described in WO12/086639, when the upper and lower busbars extend obliquely with respect to the surface-acoustic-wave propagation direction at the same angle as described in Japanese Unexamined Patent Application Publication No. 2000-286663, the oblique angle is 18° or more and 72° or less, and is too large. Therefore, a large insertion loss occurs.